Electromagnetic Attraction-Based Bulge Forming in Small Tubes: Fundamentals and Simulations

Electromagnetic forming is widely used in processing of lightweight alloys and provides significant improvements in the forming limits of materials. However, the forming coils are difficult to wind, which means that small tube bulge forming processes are quite challenging because the coil must be placed inside the tube to generate the repulsive electromagnetic force required. To solve this problem, a novel method that uses electromagnetic attraction for bulge forming is proposed. The method uses a special discharge circuit that consists of a wide pulse power supply (2 MJ/25 kV/6400 μF) and a narrow pulse power supply (25 kJ/25 kV/80 μF) to drive the forming coil to generate an attractive electromagnetic force. The proposed method was verified through numerical simulations. The results show that the final deformation could be increased by increasing the slope at the falling edge or reducing the slope at the second rising edge of the discharge current. The maximum expansion of the tube could reach 3.74 mm after parameter optimization. The method and results presented here will be helpful in the design of electromagnetic forming systems and in broadening their application to bulge forming in small tubes.